Helium isotopes in peridotite mineral phases from Hyblean Plateau xenoliths (south-eastern Sicily, Italy)
Chemical Geology(2005)
摘要
Fourteen He isotope and abundance analyses have been performed on olivine, orthopyroxene, and clinopyroxene grains from selected spinel-facies peridotite xenoliths collected from the Hyblean Plateau, southeastern Sicily. These peridotites consist of protogranular-textured, spinel-facies lherzolites and lherzolitic harzburgites. Microthermometric data on olivine and pyroxenes reveal that the fluid inclusions (FIs) are nearly pure CO2, with densities ranging from 0.76 to 1.15 g/cm3. The densest inclusion trail occurs in an orthopyroxene grain and indicates a trapping-pressure of 0.98–1.14 GPa (estimated equilibration temperature of 1000 °C for pure CO2 system) corresponding to a depth of ∼36–41 km (for an average estimated density of the lithospheric column of 2.85 g/cm3). These are minimum estimates. The near-unimodal distribution of CO2 densities indicates that these xenoliths have been stored at the pressure interval of 0.75–0.95 GPa—corresponding to a depth of ∼27–35 km (crust–mantle boundary or just below). En route to the surface, they have not had any significant interaction with shallower volatile reservoirs.
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关键词
Peridotite xenoliths,He isotopes,CO2 fluid inclusions,Mantle metasomatism,Hyblean Plateau
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